More of a thaw, really.

I think genociding natives outweighs keeping the south in line enough to put him at the bottom

You should look into the effects on causality of going faster than the speed of light. If you can send information faster than the speed of light all kinds of wacky paradoxes show their heads. I used to believe what you did, that with time and knowledge we could overcome the speed of light. But after learning more about our universe I don’t think that’s the case anymore. I enjoyed this video on the topic https://youtu.be/an0M-wcHw5A